Unit 2 Energy Changes and Rates of Reactions

First Law of Thermodynamics

States that energy can be converted from one form to another but cannot be created or destroyed

Second law of thermodynamics

States that when two objects are in thermal contact heat is transferred from the object at a higher temperature to the object at the lower temperature until both objects are the same temperature

what is the system?

The system is defined as the chemicals involved in a chemical reaction

What is the surrounding?

the surroundings are defined as everything around the system, including the solvent, beakers, thermometers, the room, and the experimenter

What are three factors that affect the quantity of heat transferred from a substance

i. Mass of a substance

ii. Specific heat capacity of the substance

III. Temperature change of the substance

explain an open system

A system that can exchange both matter and energy with its surroundings

Closed system

a system that can exchange both matter and energy with the surroundings

Define a isolated system

A system that cannot exchange either energy or matter with the surroundings

Define endothermic

Describes the process during which heat enters a system

Define exothermic

Describes the process during which heat leaves a system

Define what enthalpy is

the heat content of a system

Explain how water boiling has a +’ve enthalpy change

Because the water is gaining energy from the surroundings which results in the water turning into a gaseous state

What is calorimetry?

Calorimetry is the study of energy changes in physical or chemical reactions

What is a calorimeter

A calorimeter is a device that is used to measure the heat absorbed or released by a reaction

What is the principle of calorimetry

heat released by the reaction (system) = the heat absorbed by the calorimeter (Surroundings)

What is hess’s Law

the enthalpy change of a multistep process is the sum of the enthalpy change of its individual steps h

Standard Molar enthalpy of formation

The amount of energy gained or lost when 1 mole of a substance is formed from its elements at SATP

Chemical Kinetics

Is the branch of chemistry concerned with the rates of chemical reactions. A rate is a change in a measurable quantity over time

What does the collision theory provide?

Collison theory gives us more information about how particles interact to cause a reaction to occur

What determines if a collision is successful?

1. Particles need to have proper orientation. This refers to the direction in which they collide

2. Particles need to have a minimum amount of kinetic energy. This is called the activation energy

What is the activation energy

• This energy is used to break the existing bonds and form new bonds resulting in the rearrangement of atoms

What is the moment of collision called?

• Called the transition state where bonds are being broken and reformed; atoms are being rearranged

• Atoms are stuck to each other in “blob-like” arrangement

What is the activated complex?

• It is a high energy and very unstable arrangement of atoms that occurs right when the atoms collide

How does temperature affect the rate of reaction?

• Increasing the temperature increases the average kinetic energy of a sample, leading to

1. Increased speed of the molecules which increases the frequency of collisions

2. Increased # of molecules with the required activation energy

How does concentration affect the rate of reaction

• Increasing concentration of reactants causes increased frequency of collisions

• But only for (aq) and (g) species - because the concentration of (s) and (l) species cannot be increased significantly

How does a catalyst effect the rate of reaction?

• A catalyst is a substance that increases the rate of reaction without being used up itself

• Catalyst changes the reaction pathway so that less activation energy is required

• Increases both forward and reverse reactions

How does the nature of reactants effect the rate of reactions

• Reactions involving ions tend to proceed rapidly, whereas rates of reactions for molecules are usually slower

• In general, reactions involving (aq) and (g) react faster than (l) and (s)

How does the pressure of gas reactants affect the rate of reaction?

• For reactants that are gases, increasing the pressure (decreasing the volume) increases the frequency of collisions